1. Field of the Invention
The present invention relates to shoe sole and heel constructions and, in particular, to such constructions with fluid-filled cavities for providing cushioning and forward thrust.
2. Description of the Prior Art
Various types of shoe sole and heel constructions having fluid-containing cavities have heretofore been provided, such constructions being disclosed, for example, in U.S. Pat. Nos. 4,237,625, 4,358,902, 4,577,417, 5,375,346, 5,416,986 and 5,678,328.
These patents disclose molded outer sole and heel members, each having plural pockets, at least one of the pockets being defined, at least in part, by a downwardly projecting heel or metatarsal bulge molded in the member, and a passageway extending between the pockets. Air or other fluid, at atmospheric pressure, moves back and forth between the pockets through the passageway during movement of a person wearing the shoe.
These prior sole and heel structures have provided cushioning for the user's foot and have also provided forward thrust which facilitates walking or running movements. These downwardly projecting bulges usually, however, prevent the member from having an exterior flat portion in both the heel and sole portions of the outsole, which limits the versatility of the shoe. Additionally, these bulges can tend to produce a lateral instability in the shoe, causing the shoe to tilt laterally inwardly or outwardly in use, resulting in pronation of the wearer's feet. For example, in walking and jogging gaits, wherein the initial shoe strike is at the heel, the initial point of impact is typically at the laterally outer side of the heel, i.e., at the right side of the right heel and the left side of the left heel. Thus, there is a tendency for the fluid in the heel pocket to move from side to side, as well as forwardly toward the metatarsal pocket. Though this instability has been alleviated by providing downwardly projecting stabilizing structures adjacent to the bulges or by reconfiguring the fluid flow and bulge configurations, shoes incorporating these prior structures do not provide a flat sole or heel and, therefore, cannot be used for all applications.
Further, these exterior bulges are exposed and unprotected, and may possibly, if put in a harsh environment, such as a shop floor, be punctured by a nail or the like. The puncture hole would allow the air contained in the cavity to escape, thereby essentially destroying fluid flow between the pockets and the cushioning of the pockets.
Other shoe sole and heel structures include internal, interconnected air pockets in the midsole of a shoe. These structures suffer from, among other things, poor fluid flow from one pocket to another, thereby decreasing the cushioning efficiency of each pocket.